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Selected Issues for Nutrition and the Athlete: A Team Physician Consensus Statement

DEFINITION

Nutrition for sport is the provision of essential nutrients, including fuels and fluids, to provide energy for training, competition, recovery, and general health and wellness. The intake versus expenditure of these essential nutrients will be called energy balance. Optimum performance is promoted by adequate energy intake.

GOAL

SUMMARY

This document provides an overview of selected medical issues that are important to team physicians who are responsible for the care and treatment of athletes. It is not intended as a standard of care and should not be interpreted as such. This document is only a guide and, as such, is of a general nature, consistent with the reasonable, objective practice of the healthcare profession. Adequate insurance should be in place to help protect the physician, the athlete, and the sponsoring organization.

This statement was developed by a collaboration of six major professional associations concerned about clinical sports medicine issues; they have committed to forming an ongoing project-based alliance to bring together sports medicine organizations to best serve active people and athletes. The organizations are the American Academy of Family Physicians, the American Academy of Orthopaedic Surgeons, the American College of Sports Medicine, the American Medical Society for Sports Medicine, the American Orthopaedic Society for Sports Medicine, and the American Osteopathic Academy of Sports Medicine.

CONSULTANT

General Nutrition for Athletes

Nutrition for sport is the provision of essential nutrients, including both fluids and fuels, to provide energy for training, competition, recovery, and general health and wellness. Athletes can meet 100% of their dietary needs from a well-balanced nutrition plan that addresses performance, hydration, recovery, and health. In athletes with certain medical conditions (e.g., iron, calcium, and vitamin D deficiency), supplementation may be beneficial.

In this area of sports medicine, a sports dietitian (registered dietitian [RD] and preferably a board certified specialist sports dietetics [CSSD]) can be a member of the athletic care network. While many offer sports nutrition advice, an RD has met the minimum educational and training requirements of the Academy of Nutrition and Dietetics, formerly the American Dietetic Association. Only an RD can practice as a sports dietitian (1).

Athletes need to consume adequate energy (in the form of calories) to maintain or modify body weight and maximize health and training effects (1).

* Inadequate energy intake can result in muscle loss, increased risk of fatigue, increased risk of injury and illness, and prolonged recovery process.

* Excess energy intake can result in weight gain, which may increase body fat resulting in increased fatigue, risk of injury, and poor performance.

* Energy is gained through the consumption of a combination of carbohydrates, proteins, and fats.

Carbohydrate (CHO) recommendations for athletes range from 6 to 10 g·kg−1 body weight per day and can range from 50% to 70% of total calories [(4), Table 1].

* Replenishment immediately after training is important for subsequent optimal performance. Muscle glycogen resynthesis appears to occur most rapidly within the first 30 min postexercise and continues for up to 6 h after exercise.

* In periods of heavy training, the exact amount of CHO required may vary, depending on the athlete’s daily energy expenditure, type of sport, and environmental conditions.

Protein recommendations for endurance and strength-trained athletes range from 1.2 to 1.7 g·kg−1 body weight per day and can range from 10% to 35% of total calories [(12,14), Table 1].

* Protein consumption facilitates muscle synthesis and repair. Exercise increases rates of protein synthesis in the exercised muscle that persists for up to 72 h after vigorous activity.

* Protein recommendations can typically be met through diet alone; most athletes exceed their daily protein requirements. Protein and amino acid supplements are not necessary.

* Fluid/electrolyte balance must be addressed during fluid consumption and replacement, with consideration of the individual’s physiology, type, and duration of activity and environmental conditions.

* For workouts longer than 1 h in duration, fluids with added CHO appear to help maintain hydration and performance levels. For workouts lasting more than several hours, fluids with sodium added as well appear optimal for performance and hydration.

* Ad libitum fluid ingestion may not be sufficient to maintain hydration and performance levels, especially in young athletes; therefore, intake may be enhanced by fluids with flavor, color, carbohydrate, and sodium (5).

* Weight measurement is a good estimate of fluid loss (percent change pre- to postexercise change) to guide replacement amounts. For each pound lost during exercise, 16–24 oz of fluid need to be consumed.

Cautions

* Misinformation and/or myths about nutrition are common and come from widespread noncredible sources.

* Some athletes may experience gastric upset when attempting to implement appropriate fluid and fuel recommendations. Tolerance may be enhanced by increasing the rate of stomach emptying with the following steps:

○ Take small, frequent sips and meals rather than large volume.

○ Choose fluids with low concentrations of CHO (6%–8%) rather than water or beverages with higher CHO content.

○ Tepid fluids appear to empty more rapidly than cold fluids.

○ Some athletes will experience upset with fructose and should consider glucose- or sucrose-based CHO instead.

* When making dietary changes, consider the timing and implementation.

* In times of increased training, athletes may believe they need additional sources of protein. Higher balanced caloric intake will provide the necessary amount of protein. A common error is using protein supplementation to offset caloric deficit.

* While many practitioners refer to themselves as sports nutritionists, only those who hold the RD credential and is eligible for CSSD may practice as a sports dietitian.

Nutrition for Out-of-Season Training

Out-of-season training is defined in this document as the period an athlete is not in competition but training for that purpose. Overall nutritional principles for fluids and fuels remain the same in accordance with the goals of the off-season training regimen. These factors may be more important during out-of-season training:

* Depending on training activity, energy requirements may be increased or decreased.

* The well-balanced diet does not require protein or amino acid supplements, even during muscle-building in strength/weight training.

* Modification of energy intake for the purpose of weight gain or weight loss goals.

Nutrition for In-Season Training

In-season training is defined in this document as the period in athletic competition. Overall nutritional principles for fluids and fuels remain the same in accordance with the goals of the in-season training regimen. The following factors may be more important during in-season training:

* The distribution of fluid and fuel intake

○ Increased emphasis on CHO over protein and fat

○ Increased monitoring of fluid and electrolyte consumption and replacement

Nutrition for Weight Modification

The modification of an athlete’s weight may help optimize athletic performance and health (Tables 3 and 4). This program is best monitored by a health care provider with expertise in sports nutrition. The goals of this modification should be realistic and relate to the athlete’s gender, sport, and medical, psychological, and weight history. Weight modifications should be implemented in the off season (15). Other factors to consider for weight gain or loss include the following:

Principles of Weight Gain

* Athletes who desire to gain weight should adjust their energy intake to increase lean muscle mass, not body fat.

* Athletes who desire to gain weight should consume protein at the upper range of recommended protein level (Table 1).

* To gain lean muscle mass, an athlete must take in an additional 500–1000 kcal·d−1 along with participating in an appropriate strength training program. Either of these tasks done separately will not cause a gain in lean muscle mass. Weight gain in excess of 2–3 lb·wk−1 is not all lean muscle mass.

Caution

* Large increases in body fat may have adverse effects on the immune system and may increase risk factors for chronic disease.

* Athletes attempting to increase their body or muscle mass often use supplements purported to enhance weight gain. The only proven safe and effective means to increase muscle size and strength for long-term athletic performance is increased muscular work combined with recommended energy and protein intake.

Principles of Weight Loss

* Athletes who desire to lose weight should adjust their energy intake to maintain muscle mass and decrease body fat.

* Increases in energy expenditure and moderate decreases in energy intake may help preserve fat-free mass and muscle strength while dieting.

* Weight loss should be gradual at approximately 0.5–2.0 lb·wk−1, which equals a net negative energy balance of 250–1000 calories per day.

* Female athletes should not consume less than 1200–1400 calories per day; male athletes should not consume less than 1500–1700 calories per day. An athlete cannot maintain adequate micronutrient levels with these restrictive amounts of energy intake.

Caution

* Athletes, particularly those in lean-body sports, may experience pressure to achieve low body weights or body compositions that are unrealistic. The pressure to meet these goals can lead to disordered eating and eating disorders.

○ Negative energy balance can lead to weight loss and disruption of endocrine function (11).

○ These conditions add a unique challenge to any health care professional guiding them through the weight loss process.

* Weight loss may impair performance due to factors including a reduction in energy stores, impairment of immune function, alterations in mood, changes in enzyme activity, and structural alterations in muscle.

Preexercise Nutrition

Exercise refers to targeted training or competition, potentially with sport-specific requirements. Preexercise is defined as 4 h or less before the exercise session. General nutrition and in-season requirements for fluids and fuels apply before this time. Adequate nutrition before exercise has been shown to improve performance, as compared to a fasting state (10). The preexercise fuel and fluids should be composed primarily of CHO to maintain BG during exercise, which leads to a sparing of muscle and liver glycogen, and moderate in protein and low in fiber and fat to minimize gastrointestinal distress (1).

Preexercise meals should be individualized, and differences need to be recognized. Optimal timing is not always practical, based on scheduling or individual preferences. Athletes should experiment with fluid and fuel choices and the timing of consumption while training before using the strategies during competition.

The timing of fluid and fuel intake is important when considering pre-exercise nutrition.

* Fluids

○ At least 4 h before exercise, drink 12–20 oz (350–600 mL) of water or sports drink (6%–8% CHO [14–19 g per 8 oz], Table 5). This will optimize hydration and allow adequate time for excretion of any excess fluid.

Nutrition during Exercise

During extended exercise, energy stores in the body are depleted, thirst sensation may be dulled, and the rate of gastric emptying may be reduced. Therefore, athletes need to consume both fluids and fuel for optimal performance. As glycogen stores in the body are being depleted, muscles rely more heavily on blood glucose for fuel, especially after 2–4 h of continuous exercise. In addition, adequate fluid and electrolyte replacement is necessary for proper cardiovascular function, thermoregulation, optimal performance, and recovery and may help prevent muscle cramping and electrolyte imbalance. An individualized plan is necessary to prevent overhydration, dehydration, and/or electrolyte imbalances.

* Fluid replacement should begin early during an exercise program and continue during activity.

* For exercise lasting less than 1 h, water or sport drink is sufficient.

* CHO consumption is especially important when exercising after an overnight fast or when liver glycogen is decreased.

* Consumption of 30–60 g CHO per hour has been shown to extend endurance performance for longer events (3).

○ Consumption of 6–12 oz of sports drink every 15–30 min during exercise can extend exercise capacity of athletes who participate in prolonged or intermittent sports.

○ Fluid replacement with water alone may lead to hyponatremia. Athletes should avoid drinking too much water and only drink as much fluid as they have lost during exercise. Consuming beverages with at least 100 mg of sodium per 8 oz will help prevent hyponatremia.

* Fluid and electrolyte losses will vary depending on the sport, the individual, and the environmental conditions. The athlete should attempt to anticipate the losses as a guide to fluid intake during exercise.

* Potassium is important for fluid and electrolyte balance. A diet rich in a variety of fresh fruits, nuts, seeds dairy foods, lean meats, and whole grains is usually considered adequate for maintaining normal potassium status among athletes

Caution

* Athletes should not begin exercise in an energy-depleted or dehydrated state.

* Both protein and potassium consumption during exercise is unnecessary for performance.

* CHO in solid form can also be consumed during exercise, but digestion is slower compared to liquid and gel forms. It is easier to consume solid carbohydrates in certain sports such as cycling, whereas athletes in other sports such as running and swimming may find it easier to consume carbohydrates in liquid form.

* Fluid in hyperhydrated forms (e.g., glycerol) does not improve performance or hydration and is not recommended.

Nutrition for Postexercise Recovery

After exercise, there may be deficiencies in fuels (primarily muscle and liver glycogen) and fluids (water and electrolytes). There may also be muscle damage, requiring protein for repair. The postexercise dietary goals are to provide adequate CHO, fluids, and electrolytes to replace muscle glycogen, aid recovery, and restore hydration. Protein consumption after exercise will provide amino acids for building and repair of muscle tissue.

Restoration of these deficiencies is a requirement for optimal performance in the next exercise event. The method by which this restoration occurs is influenced by the timing of the next competition. This is particularly critical for athletes who have multiple, same-day exercise (e.g., tournaments, two-a-days) or next-day exercise.

The window for optimal postexercise recovery is 6 h after the cessation of that exercise. Most glycogen resynthesis begins within the first 30 min.

* Intake of 1.0–1.5 g CHO per kilogram within 30 min after exercise increased glycogen storage and decreased recovery time (muscle strength) compared to ingestion two hours after exercise (8).

* CHO with a high glycemic index (e.g., simple CHO) result in an increase in the rate of resynthesis compared to CHO with a low glycemic index (e.g., complex CHO) (2) (see Table 6).

* Adding 10–20 g of protein to a postexercise recovery snack will not enhance muscle glycogen stores, but it will support muscle repair and growth. It is important to include both carbohydrates and protein in a recovery regimen. Adding 10–20 g of protein postexercise will help start protein synthesis (9).

To continue recovery beyond the 30-min window, an athlete should eat a 1.0- to 1.5-g CHO per kilogram and 10–20 g of protein approximately 2 h postexercise. See Table 7.

In conjunction with the need for glycogen replacement, fluid replacement is necessary to optimize recovery.

* Volume of replacement should be 1.5 times the amount of fluid lost. A simple guideline of consuming 16–24 oz of fluid for every pound lost during exercise can help athletes replace fluids quickly postexercise.

* Thirst is not a good indicator of fluid status: 1.5-L loss is required before thirst is perceived.

* Addition of electrolytes speeds the rate of recovery; individual fluid balance may be restored approximately three times faster with sports drink as compared to water. Consuming rehydration beverages and salty foods as subsequent meals/snacks will help replace fluid and electrolyte losses.

* Water plus food is a good replacement strategy, provided that food can be consumed. Food has a higher electrolyte concentration than electrolyte drinks.

* There is significant variance in individual sweat rates and electrolyte loss due to environmental conditions, inadequate acclimatization, or individual variances.

* If high sweat rates or electrolyte losses are present (e.g., “salty sweaters”), additional sodium replacement may be necessary.

* Replacement should stop approximately 0.5–1 h before the next competition to allow homeostasis.

Supplementation

* Athletes can meet 100% of their dietary needs from a well-balanced nutrition plan that addresses performance, hydration, recovery, and health. In athletes with certain medical conditions (e.g., iron, calcium, and vitamin D deficiency), supplementation may be beneficial.

* Although all manufacturers are required by the Food and Drug Administration to analyze the identity, purity, and strength of all their product’s ingredients, they are not required to demonstrate the safety and efficacy of their products.

REFERENCES

1. American College of Sports Medicine Position Stand. Nutrition and athletic performance. American Dietetic Association; Dietitians of Canada; American College of Sports Medicine. Med Sci Sports Exerc. 2009; 41 (3): 709–31.

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